Planar Waveguide Filter for CMOS Pixel Diffraction Loss
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Solution Overview
Problem
As complementary metal-oxide semiconductor (CMOS) image sensors are scaled down, diffraction effects from scaled-down microlenses can negatively impact the quantum efficiency (QE) of these sensors.
Innovation Solution
The implementation of a wave guide filter with a substantially planar upper surface, which includes a light filter disposed in a light filter grid structure. The light filter and grid structure are at least partially translucent and have refractive indices that facilitate the guidance of incident light onto the photodetectors, thereby reducing diffraction effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CMOS image sensors are scaled down to reduce size and cost, then manufacturing cost and device size are reduced, but diffraction effects from scaled-down microlenses negatively impact quantum efficiency
Solution Approach 1:
The patent introduces a waveguide filter as an intermediary component between the microlens and photodetector. This waveguide filter captures diffracted light that would otherwise be lost and guides it to the photodetector, thereby recovering quantum efficiency without requiring larger microlenses. The waveguide filter acts as a mediator that converts the harmful diffraction effect into useful light guidance.
Solution Approach 2:
The patent changes the optical parameters of the light guidance system by replacing traditional microlens-based guidance with a waveguide filter system. The waveguide filter uses total internal reflection and refraction at controlled angles to guide light, fundamentally changing how light is directed to the photodetector and eliminating dependence on microlens size for light collection efficiency.
2Quantity of substance
If microlenses are scaled down to match smaller pixel dimensions, then pixel density is increased, but light guidance capability deteriorates due to enhanced diffraction effects
Solution Approach 1:
The waveguide filter serves as an intermediary that decouples pixel density from light guidance capability. By introducing this intermediate optical component, the system can maintain high pixel density with small features while the waveguide filter handles the light guidance function independently, preventing the deterioration of light guidance as pixel size decreases.
Solution Approach 2:
The patent transitions from three-dimensional microlens-based light guidance to a two-dimensional waveguide filter plane. The waveguide filter operates in a planar configuration with light entering at specific angles and being guided through total internal reflection, effectively adding a dimensional change to the light guidance approach that is less sensitive to feature size scaling.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The wave guide filter improves the quantum efficiency of CMOS image sensors by effectively guiding incident radiation onto the photodetectors, thus mitigating the negative impact of diffraction from scaled-down microlenses.
Implementation Method 1
The light filter and grid structure are at least partially translucent and have refractive indices that facilitate the guidance of incident light onto the photodetectors
Implementation Method 2
The wave guide filter is configured to guide incident radiation toward the photodetectors
Data Source
AI summary
In some embodiments, an image sensor is provided. The image sensor includes a photodetector disposed in a semiconductor substrate. A wave guide filter having a substantially planar upper surface is disposed over the photodetector. The wave guide filter includes a light filter disposed in a light filter grid structure. The light filter includes a first material that is translucent and has a first refractive index. The light filter grid structure includes a second material that is translucent and has a second refractive index less than the first refractive index.